t_(8/5)对X90管线钢焊接热影响区细晶区显微组织的影响

Influence of t_(8/5) on the Microstructure in HAZ Fine Grain Zone of X90 Pipeline Steel

为了研究焊接冶金与热循环过程对X90管线钢焊接热影响区细晶区显微组织的影响,采用淬火变形膨胀仪模拟了不同t8/5条件下X90管线钢热影响区细晶区的热循环过程,并在光学显微镜和扫描电子显微镜下观察了其显微组织随t8/5不同而变化的情况。研究结果表明,当t8/512 s时,X90管线钢组织以多边形铁素体为主,并随着t8/5的减小,会先后出现珠光体和粒状贝氏体;当t8/5控制在6~12 s时,细晶区组织主要为性能良好的贝氏体组织和少量准多边形铁素体。为获得综合性能优异的焊接接头,冷却过程中焊接热影响区细晶区的t8/5应控制在6~12 s更为合适。

In order to study the influence of the welding metallurgy and heat cycle process on microstructure in HAZ fine grain zone of X90 pipeline steel, the heat cycle process was simulated by quenching deformation expansion instrument under different t8/5 conditions, and the microstructure change was observed by the optical microscope （OM） and scanning electron microscopy （SEM）. The results showed that a mixed microstructure containing granular bainite （GB）, bainite ferrite （BF） and lath martensite （LM） appear under the condition of a t8/5 less than 6 s ;the microstructure was predominantly polygon ferrite （PF）when t8/5 is more than 12 s,and with the decrease of the t8/5,pearlite（P） and granular bainite（GB） will appear successively. Only when the t8/5 was limited in 6-12 s,the microstructure of fine grain zone was bainite（B） dominantly and is accompanied by a small quantity of quasi-polygonal ferrite （QF）. In order to obtain excellent comprehensive properties of welded joint, the t8/5 in HAZ fine grain zone during the cooling process should be controlled in 6-12 s.